In many small factories the manufacture takes place at different workstations. The workstations may contain one or several fixed machines, a fixture for holding work pieces, or a table. The production can be speeded up if an industrial robot is used to carry out work at the workstations.
WO2010/043640 discloses a robot for performing work at a plurality of workstations. The robot controller is positioned on a movable platform. Each workstation is provided with a docking station to provide a defined and fixed position for the robot in relation to the machine at the workstation. The platform with the robot is moved between the workstations. When the platform with the robot reaches one of the workstations, the platform is attached to the docking station positioned at the workstation. When the robot has finished the work at the workstation, the platform is detached from the docking station, and the platform with the robot is moved to the next workstation.
In factories flexibility and space are important, robot systems need to follow safety regulations to protect humans from injury. Normally fences and doors with safety monitoring are used to meet safety requirements. Fences are in the way and block the machine and take up space.
In order to avoid fences around a robot cell, safety sensors are used in combination with a safety robot motion supervision system and a safety control unit. It is known to have one or more safety zones defined in relation to the sensors, and arranged to detect if a human is entering any of the safety zones. The safety control unit is configured to adjust the speed of the robot upon detecting that a human is entering any of the safety zone. If there is more than one safety zone, the speed of the robot is reduce to zero when the human enters the safety zone closest to the robot.
Fenceless robot system using laser scanners to detect workspace intrusion is, for example, known from “The Shrinking Footprint of Robot Safety” by Tanya M. Anandan, Robotic Industries Association, posted 10/06/2014 October 14-16: robotics.org, “The Shrinking Footprint of Robot Safety”.
The robot and the workstation at which the robot performs work are positioned on a movable platform. Four laser scanners are installed at the corners of the movable platform and close to the floor. The laser scanners are scanning horizontally for any approach to the system. As an intrusion gets closer, these scanners tell the robot system to operate slower. In this robot system the robot is performing work on the movable platform and accordingly the working area of the robot is outside the range of the sensors.
However, in most applications, the working area of the robot extends outside the movable platform. A problem with such a robot system is that the sensors cannot distinguish between the robot and a human moving in the working area of the robot. This problem can, for example, be solved by the software safety controller since the position of the robot is known. Another problem is that the movable robot arm can hide the sensor if the robot is working close to the sensor and by that prevent the sensor from sensing a part of the working area.
A problem with having four laser scanners is that they are very expensive. Thus, there is a desire to reduce the number of laser scanners.
US2008021597 discloses an apparatus and method for protection of a robot, having a safety sensor system for detection of objects in the working area of the robot, and a safety controller which interacts with a robot controller based on signals from the safety sensor system. The safety sensor system has a large number of non-contacting proximity sensors fitted to the base of the robot so that a safety-relevant part of the working area of the robot is covered by the detection areas of the proximity sensors. Further, a laser scanner is fitted to the base of the robot and arranged to monitor a rearward part of the working area. The laser scanner together with the non-contacting proximity sensors approximately cover the working area of the robot. Due to the large number of proximity sensors, there is no problem if one of the sensors is hidden since the other sensors will be able to detect an intrusion of human.
US20130268118 discloses a robot system comprising a movable platform provided with drive tracks, a drive system configured to maneuver the movable platform over a work surface, and two articulated robot arms attached to the platform. Each of the articulated robot arms are provided with grippers and sensors, such as gripper cameras. The platform is provided with one or more sensors mounted on the platform to have a field of view directed forward in order to detect obstacles in the direction of movement of the platform.